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A chance discovery in an old German book may have overturned our understanding of how crystals grow.

The defining feature of a crystal is that it is composed of a pattern of atoms that repeats in all directions with perfect symmetry. This neat structure makes it possible to diffract X-rays through crystals to reveal the pattern inside 鈥� a technique instrumental in understanding the atomic structure of many important drugs, like penicillin.

But X-ray diffraction is very difficult to apply to small crystals 鈥� and as a result we have long been unsure of what crystals look like when they begin to grow.

Bart Kahr at New York University has been trying to solve this puzzle since 2007, when he came across a 1929 book called 鈥淕edrillte鈥� Kristalle, which described how many tiny crystals had helical shapes. Gedrillte is German for 鈥渄rilled鈥�, and so was perhaps intended to signify how the crystals resembled helical drill bits.

This was a big surprise to Kahr. Crystals tend to have straight sides and geometric shapes. 鈥淚 asked everybody in the world about this,鈥� says Kahr. 鈥淣obody knew what the heck I was talking about.鈥�

He began investigating and soon confirmed that . Over the past decade, he and his colleague have found about 150 examples, and Kahr says there are about another 100 reported by other scientists.

He has now found twisting in common over-the counter drugs, including aspirin, paracetamol and . 鈥淭he point was to emphasise how something so common can be so poorly appreciated,鈥� says Kahr.

His work has been 鈥渞eally great at focusing on the very thin, hair-like crystals that nobody could solve and that tended to be ignored鈥�, says Sally Price at University College London.

鈥淚 find it fascinating that such twisted structures may be a precursor to non-twisted crystals,鈥� says Matthew Fuchter at Imperial College London. 鈥淭he fact a given structure grows twisted only to then unwind as it becomes larger is amazing.鈥�

All this raises a question: how do crystals go from being twisted when they are tiny, to straight when they are larger? This is an 鈥渋ntellectual chasm鈥�, says Kahr, and one that he is now starting to investigate.

鈥淭wisting is surely teaching us what is a crystal, especially in the early stages of growth, and that is foundational, so who knows what it could eventually explain,鈥� says Kahr.